This section is intended to introduce the reader to various aspects of art which may be related to various aspects of the present invention which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements is are to be read in this light, and not as admissions of prior art.
A wireless LAN (WLAN) is a flexible data communications system implemented as an extension to, or as an alternative for, a wired LAN within a building or campus. Using electromagnetic waves, WLANs transmit and receive data over the air, minimizing the need for wired connections. Thus, WLANs combine data connectivity with user mobility, and, through simplified configuration, enable movable LANs. Some industries that have benefited from the productivity gains of using portable terminals (e.g., notebook computers) to transmit and receive real-time information are the digital home networking, health-care, retail, manufacturing, and warehousing industries.
Manufacturers of WLANs have a range of transmission technologies to choose from when designing a WLAN. Some exemplary technologies are multicarrier systems, spread spectrum systems, narrowband systems, and infrared systems. Although each system has its own benefits and detriments, one particular type of multicarrier transmission system, orthogonal frequency division multiplexing (OFDM), has proven to be exceptionally useful for WLAN communications.
OFDM is a robust technique for efficiently transmitting data over a channel. The technique uses a plurality of sub-carrier frequencies (sub-carriers) within a channel bandwidth to transmit data. These sub-carriers are arranged for optimal bandwidth efficiency compared to conventional frequency division multiplexing (FDM) which can waste portions of the channel bandwidth in order to separate and isolate the sub-carrier frequency spectra and thereby avoid inter-carrier interference (ICI). By contrast, although the frequency spectra of OFDM sub-carriers overlap significantly within the OFDM channel bandwidth, OFDM nonetheless allows resolution and recovery of the information that has been modulated onto each sub-carrier.
The transmission of data through a channel via OFDM signals also provides several other advantages over more conventional transmission techniques. Some of these advantages are a tolerance to multipath delay spread and frequency selective fading, efficient spectrum usage, simplified sub-channel equalization, and good interference properties.
In an OFDM receiver with multiple receiving antennas or multiple transmission channels available it may be beneficial to be able to select an antenna or channel that provides better reception according to some predetermined criterion. One example of a selection process that may be used is to estimate the bit error rate (BER) of each available antenna or channel and pick the antenna or channel that exhibits the lowest BER estimate. However, a direct BER estimation may require a significant amount of processing time and may not be desirable or feasible in some systems, in particular in bursty transmission systems.
One traditional approach to identifying an antenna or channel that is likely to provide a low BER has been to look at the average signal power of the multiple subcarriers being received. The average signal power does not, however, necessarily translate unequivocally into a corresponding BER because channels having the same average power can have different shape of the channel response. Accordingly, different BERs may be obtained in subsequent stages of the receiver. A method and apparatus for identifying the antenna or channel in an OFDM receiver that is likely to provide a low BER based on antenna or channel response characteristics is desirable.